High speed print hammer and bar magnet means



Nov. 15, 1966 c. J. HELMS ETAL 3,235,166

HIGH SPEED PRINT HAMMER AND BAR MAGNET MEANS Filed Dec. 18, 1964 2Sheets-Sheet 1 By MMI/QQMJ cum 4% 3,285,166 HIGH SPEED PRINT HAMMER ANDBAR MAGNET MEANS 18, 1964 Nov. 15, 1956 c. J. HELMS ETAL 2 Sheets-Sheet2 Filed Dec.

United States Patent 3,285,166 HIGH SPEED PRINT HAMMER AND BAR MAGNETMEANS Clifford J. Helms, Woodland Hills, and Leo J. Emenaker, Playa DelRey, Calif., assignors to Data Products Corporation, Culver City,Calif., a corporation of Delaware Filed Dec. 18, 1964, Ser. No. 419,5092 Claims. .(Cl. 101-93) This invention relates generally to electricallycontrolled high speed printing apparatus and more particularly to animproved electromagnetically operated hammer assembly for use in suchapparatus.

High speed printing devices utilizing rotating printing drums are wellknown in the prior art. Typically, such drums have alphabetic and/ornumeric printing characters on the surface thereof arranged in columnarfashion. More particularly, the drum is provided with a plurality ofcircumferential tracks equal to the maximum number of characters to beprinted on any one line and each such track includes one full set ofcharacters which the particular printing device is adapted to print.

In such printing devices, a hammer assembly is associated with eachcircumferential track and includes a hammer or impact device which canbe caused to strike a selected character during the rotation of the drumin response to appropriate control signals. An inked ribbon and a paperstrip upon which data is to be printed are usually positioned betweenthe drum and the hammers. Each hammer, when actuated, thus strikes theback of the paper strip thereby forcing the paper strip against theribbon, and the ribbon in turn against the character on the drum toconsequently print the selected character on the front of the paperstrip.

Typical prior art hammer assemblies consist of a movable impact devicewhich is associated with a solenoid such that upon energization of thesolenoid coil, a solenoid armature is driven against the impact deviceto thereby propel it against the paper. In attempting to significantlyincrease the speed of printing devices, problems arise involving thecoupling between the solenoid armature and the impact device and in aneffort to solve these problems, improved hammer assemblies have beenintroduced, as for example disclosed in US. Patent Number 3,087,421. Thehammer assembly disclosed in the cited patent avoids coupling problemsby mounting a magnetic coil directly on the impact device andassociating the coil with a permanent magnettic field such thatenergization of the coil develops a magnetic field which interacts withthe permanent magnetic field to propel the impact device against thepaper strip.

A still further improvement in hammer assemblies is disclosed in US.Patent No. 3,172,352 for -a Printing Hammer Assembly by Clifford J.Helms, which also utilizes the concept of mounting a coil on an impactdevice but which, in addition, introduces improved means for supportingthe impact device. Inasmuch as it is desired that the printed charactersbe spaced by a certain small distance, it is of course essential thatthe impact devices be correspondingly spaced. Because of the physicalsize of each hammer assembly including the impact device, its supportingmeans, and the permanent magnets associated therewith, it has beenimpossible to space the impact devices sufiicien-tly close in a singletie-r. Consequently, it has been the practice to stagger the tiers withall of the impact devices projecting forward to the same line relativeto the printing drum. As a result, it has been exceedingly diflicult toreduce the physical size of the impact devices and since the contacttime of each impact device against the printing surface is related toits size (mass), this has represented a limiting factor on the overalloperating speed of the printing apparatus.

The improved support means disclosed in the aforecited patentapplication permits the impact devices in each tier to be more closelypackaged than in prior arrangements thus permitting :a'reduction in thenumber of tiers required and a consequent reduction in the size of eachimpact device.

Although the improvements introduced by US. Patent No. 3,172,352represent a significant advance over the state of the art, a continuingeffort has been made to still further reduce the size of the impactdevices to enable the printing apparatus to be operated even morerapidly.

It is thus an object of the present invention to provide an exceedinglyfast printing apparatus.

It is a more particular object of the present invention to provide animproved electrically controlled hammer assembly in which the impactdevices thereof can be operated more rapidly than in prior art hammerassemblies.

Briefly, in accordance with the present invention, an improved permanentmagnet arrangement is disclosed for providing a magnetic field forinteracting with the mag netic field generated by the impact devicecoils. More particularly, in lieu of providing -a pair of opposedpermanent magnets for each impact device as disclosed in the aforecitedPatent No. 3,172,352, a plurality of serially arranged permanent magnetsare provided which form a single closed magnetic loop around all of theimpact device coils. Aligned pairs of slots are defined in opposed sidesof the single loop, each slot pair adapted to accommodate a singleimpact device coi-l. By developing a permanent magnetic field in thismanner, slots for accommodating the impact device coils can be definedmuch more closely than has heretofore been possible thus reducing thenumber of impact device tiers required. Consequent ly, the impactdevices need not be as long or massive and thus they can be ope-ratedmore rapidly. By reducing the size of the impact device, the efiiciencyof the apparatus is of course also increased inasmuch as less power isrequired to print each character.

It is a still further object of the present invention to provide amethod of efficiently and inexpensively fabricating the permanent magnetarrangement of the present invention.

The novel features that are considered characteristic of this inventionare set forth with particularity in the appended claims. The inventionitself both as to its organization and method of operation, as Well asadditional objects and advantages thereof, will best be understood fromthe following description when read in connection with the accompanyingdrawings, in which:

FIGURE 1 is a side sectional view, partially broken away, of a printingapparatus constructed in accordance with the present invention;

FIGURE 2 is a diagrammatic horizontal sectional view taken substantiallyalong the plane 22 of FIGURE 1 illustrating the orientation of theimpact devices and the arrangement of the permanent magnets;

FIGURE 3 is a vertical sectional view taken substantially along theplane 33 of FIGURE 1; and

FIGURES 4(a)-(f) comprise a series of illustrations showing a preferredmethod of fabricating a permanent magnet arrangement useful in theapparatus of FIG- URE 1.

Attention is now called to FIGURE 1 which illustrates a printingapparatus in accordance with the present invention. The apparatusincludes a printing surface preferably in the form of a rotatable drum10 having a plurality of circumferential tracks thereon, each trackincluding each of the characters to be printed by the apparatus. Thedrum 10 is positioned so as to rotate past an inked ribbon 12. A stripof paper 14 upon which charv of the tracks on the printing drum.aforecited patent application, each hammer assembly bon 12.

A different hammer assembly 16 is provided for each As disclosed in the'tively connected to the support members 20. Each of the support members20 has a sleeve 24 secured thereto which sleeves are adapted to bereceived in a V-shaped positioning receptacle 26 defined on the edge ofbase plates 28 and 29. Since it is usually desired to print charactersspaced by about 0.1 inch, the impact devices must be spaced by this samedistance. In order to permit this, two groups of interleaved hammerassemblies are provided with the support members 20 of the first groupdepending from base plate 29 and the support members of the second groupprojecting upwardly from base plate 28.

In order to propel the impact device 18 against the paper strip 14,current can be applied to the conductive support members 20 to thusdrive current through the conductor of the coil assembly 22 to therebydevelop a magnetic field extending substantially perpendicularly to theplane of the impact device. The magnetic field provided by the coilassembly 22 interacts with a magnetic field provided by a permanentmagnet assembly to thus propel the impact device 18 against the paper14. Four magnet assemblies are provided. Two of the magnet assemblies30, 32 are secured to base plate 29 and respectively provide magneticfields interacting with the upper portions of the coil assemblies in thefirst and second groups of hammer assemblies. Magnet assemblies 36 and38 are supported on base plate 28 and provide fields interacting withthe lower portions of the coil assemblies. Essentially, the magnetassemblies provide a field extending in a first direction forward ofeach coil assembly and a field extending in a second direction to therear of each coil assembly. When the impact device is to be propelled,

its coil is energized to develop a field which tends to align itselfwith the field extending in the first direction.

Attention is now called to FIGURE 2 which illustrates two of the magnetassemblies each of which can be seen to be comprised of a series ofsmall permanent bar magnets 40 laid end to end on a base 42. Moreparticularly, each of the magnet assemblies is comprised of first andsecond rows 44 and 46 of small bar magnets 40. The magnets 40 of row 44are all poled similarly and positioned so as to define slots 48therebetween. The magnets 40 of row 46 are also poled similarly butopposite to the poled orientation of row 44. The magnets 40 of row 46define slots 48 which are in alignment with the slots defined in row 44.A magnetic bridging bar 50 couples the last magnet 40 in row 44 to thefirst magnet 40 in row 46 and similarly a bridging bar (not shown)provides a magnetic path between the last magnet 40 of row 46 and thefirst magnet 40 of row 44. Thus, each of the magnet assemblies defines asingle closed magnetic loop including a plurality of aligned slots.

The coil assembly 22 of a different hammer assembly is adapted to bereceived in each pair of aligned slots defined in each of the magnetassemblies. Thus, start ing from the leftmost hammer assembly 16 inFIGURE 3, it can be noted that the coil of the first hammer assemblyprojects into the first slots defined in magnet assemblies 30 and 36.The coil of the second hammer assembly projects into slots defined inmagnet assemblies 32 and 38. The coil of the third hammer assemblyprojects into slots defined in the magnet assemblies 30 and 36 and soforth. This interleaving of hammer assemblies from each of the twogroups is continued for the full stack of hammer assemblies. Thus, ifthe slots defined in each of the magnet assemblies are spaced by 0.2inch, the impact devices are actually spaced by 0.1 inch. Of course, thespacing of the characters to be printed corresponds to the spacing ofthe impact devices. The magnet assemblies illustrated in FIGURES 1through 3 can be formed by merely providing a base plate 42 and adheringa series of permanent bar magnets 40 thereto with some adhesive such asepoxy. Although a structure so formed could adequately function ascontemplated, the positioning of so many small bar magnets as preciselyas necessary would be very costly. Consequently, a method of efiicientlyand inexpensively fabricating a magnet assembly of the type illustratedin FIGURES 1 through 3 such that the desired precision can be gained bymachining rather than by positioning small parts, is illustrated inFIGURE 4.

The magnet assemblies of FIGURES 1 through 3 can be fabricated byinitially providing a T-shaped bar 60 having a length equal to that ofthe entire hammer assembly stack. The bar 60 is preferably formed of anonmagnetic material such as aluminum. A pair of long bars 62 and 64formed of permanent magnetic material can then be adhered on theshoulders 66 and 68 respectively of the bar 60. In addition, a pair ofbridging bars 70 and 72 of magnetic material are adhered between theends of the bars 62 and 64. Subsequently, a vertical hole is formed, asby drilling, through the center of the T- shaped bar at each positionwhere a slot is desired. As previously noted, the spacing betweenadjacent slots can be on the order of 0.2 inch. If the slot width isabout 0.04 inch, a total of 0.16 inch of permanent magnetic materialwill exist around the slot. Using Alnico VIII, these dimensions permit afield strength on the order of 4500 gauss to be established in the slot.After the holes 74 are formed, the slots can be formed by grinding,milling, or sawing through the center line of each hole 74 along a lineextending perpendicular to the block 60.

After the structure of FIGURE 4(e) has been thus fabricated, a pair ofwindings can be threaded through each of the holes 74. By driving acurrent through the windings in the directions indicated by the arrowsin FIGURE 4(f), the segments of the bars 62 and 64 will be magnetized inthe direction shown in FIGURE 4(a). Thus, by following the method stepssuggested in FIG- URE 4, a magnet assembly of the type useful in theprinting apparatus of FIGURE 1 can be easily and inexpensivelyfabricated.

From the foregoing, it should be appreciated that an improved permanentmagnet assembly has been disclosed herein for use in hammer assembliesin high speed printing apparatus. More particularly, by providing amagnet arrangement comprised of a series of bar magnets forming a singleclosed loop, the slots in each magnet assembly can be defined moreclosely than in prior art assemblies where a closed magnetic loop wasformed around each coil assembly; as shown, for example, in theaforecited Patent No. 3,172,352. As previously pointed out, by enablingthe slots in each magnet assembly to be positioned more closely, thenumber of magnet assembly tiers can be reduced enabling the length (andmass) of the impact devices to be reduced to thus permit a consequentreduction in travel and impact time of the impact device. A stillfurther advantage is attained by reducing the required number of hammerassembly tiers to two and that is that only one type of impact device isre quired. More particularly, it should be apparent that all of theimpact devices of FIGURE 1 are identical with those suspended from baseplate 29 having their coil assembly toward the rear and those mounted onbase plate 28 being reversed and having their coil assembly toward thefront. Where more than two tiers are used, as shown in the aforecitedPatent No. 3,172,352, difierent types of impact devices, i.e. impactdevices having their coil assemblies at different positions must beprovided. I

In addition to the fabrication advantages mentioned, the assembly ofFIGURE 4 has excellent heat dissipation characteristics inasmuch as thethermal resistance from the coil to the magnets and vertical portion ofbar 60 is lower than in prior arrangements because a greater area ofmaterial exists immediately adjacent the slots. Since the magnets arefit flush on two surfaces against the bar 60, the thermal resistancetherebetween is low thereby providing a large metal block exposed to theambient air. The holes 74 further enhance heat dissipa tion.

What is claimed is:

1. In a high speed printing apparatus including a plurality of impactdevices, each device having means thereon for selectively generating amagnetic field, an assembly for providing a permanent magnetic fieldadapted to interact with said selectively generated magnetic field, saidassembly comprising a base formed of a nonmagnetic material and havingan inverted T-shaped cross-section defining an upwardly extendingcentral bar and first and second shoulders extending substantiallyperpendicularly therefrom;

a plurality of equally spaced slots defined in said central barextending substantially perpendicularly thereto;

a plurality of permanent bar magnets each having first and secondsubstantially perpendicular surfaces;

means securing said bar magnets to said base in physical alignment andin series magnetically with said first and second surfaces of each ofsaid bar magnets respectively engaging said central bar and one of saidshoulders;

space defined between each pair of adjacent bar magnets in alignmentwith a different one of said slots;

each of said means for selectively generating a magnetic field extendinginto a different one of said spaces and the slot aligned therewith.

2. In a high speed printing apparatus including a plurality of impactdevices, each device having a coil thereon adapted to be selectivelyenergized to generate a magnetic field, an assembly for providingpermanent magnetic fields adapted to interact with said selectivelygenerated magnetic fields, said assembly comprising a base formed of anonmagnetic material and having an inverted T-shaped cross-sectiondefining an upwardly extending central bar and first and secondshoulders extending substantially perpendicularly therefrom;

a plurality of equally spaced slots defined in said central barextending substantially perpendicularly thereto;

a plurality of permanent bar magnets each having first and secondsubstantially perpendicular surfaces;

means securing a first group of said bar magnets to said base with saidfirst and second surfaces of each of said bar magnets in said firstgroup respectively engaging said central bar and a first of saidshoulders, said first group of bar magnets being arranged to define aspace between each pair of adjacent bar magnets which spaces are inalignment with said slots;

means securing a second group of said bar magnets to said base with saidfirst and second surfaces of said of each bar magnets of said secondgroup respectively engaging said central bar and a second of saidshoulders, said second group of bar magnets being arranged to define aspace between each pair of adjacent bar magnets which spaces are inalignment with said slots;

means supporting said impact devices so that each of said coils extendsinto a different slot and a pair of spaces in said first and secondgroups aligned therewith;

said bar magnets in said first group being oriented in seriesmagnetically to define a magnetic field extending in a first directionforward of each of said coils and said bar magnets of said second groupbeing oriented in series magnetically to define a magnetic fieldextending in a second direction to the rear of said coils; and first andsecond bridging bars respectively magnetically coupling the end magnetof said first group to the adjacent end magnet of said second group andthe end magnet of said second group to the adjacent end magnet of saidfirst group.

References Cited by the Examiner UNITED STATES PATENTS 2,686,470 8/1954Gore et al. 101-93 2,853,940 9/1958 Wockenfuss et al 101-93 2,958,93111/1960 Hurt 29-15561 2,997,632 8/1961 Shepard 101-93 3,002,263 10/1961Feinberg et al 29-155.61 3,087,421 4/ 1963 Irwin et al. 101-93 3,164,0851/ 1965 Hawkins 101-93 3,172,352 9/1965 Helms 101-93 3,172,353 9/1965Helms 101-93 ROBERT E. PULFREY, Primary Examiner.

E. S. BURR, Assistant Examiner.

1. IN A HIGH SPEED PRINTING APPARATUS INCLUDING A PLU RALITY OF IMPACTDEVICES, EACH DEVICE HAVING MEANS THEREON FOR SELECTIVELY GENERATING AMAGNETIC FIELD, AN ASSEMBLY FOR PROVIDING A PERMANENT MAGNETIC FIELDADAPTED TO INTERACT WITH SAID SELECTIVELY GENERATED MAGNETIC FIELD, SAIDASSEMBLY COMPRISING A BASE FORMED OF A NONMAGNETIC MATERIAL AND HAVINGAN INVERTED T-SHAPED CROSS-SECTION DEFINING AN UPWARDLY EXTENDINGCENTRAL BAR AND FIRST AND SECOND SHOULDERS EXTENDING SUBSTANTIALLYPERPENDICULARLY THEREFROM; A PLURALITY OF EQUQLLY SPACED SLOTS DEFINEDIN SAID CENTRAL BAR EXTENDING SUBSTANTIALLY PERPENDICULARLY THERETO; APLURALITY OF PERMANENT BAR MAGNETS EACH HAVING FIRST AND SECONDSUBSTANTIALLY PERPENDICULAR SURFACES; MEANS SECURING SAID BAR MAGNETS TOSAID BASE IN PHYSICAL ALIGNMENT AND IN SERIES MAGNETICALLY WITH SAIDFIRST AND SECOND SURFACES OF EACH OF SAID BAR MAGNETS RESPECTIVELYENGAGING SAID CENTRAL BAR AND ONE OF SAID SHOULDERS; SPACED DEFINEDBETWEEN EACH PAIR OF ADJACENT BAR MAGNETS IN ALINGNMENT WITH A DIFFERENTONE OF SAID SLOTS; EACH OF SAID MEANS FOR SELECTIVELY GENERATING AMAGNETIC FIELD EXTENDING INTO A DIFFERENT ONE OF SAID SPACES AND THESLOT ALIGNED THEREWITH.